The invention relates to a trailer electronic braking system for motor vehicles having a plurality of trailers.
In Australia and North America, vehicles consisting of a tractor unit and two or more trailers are commonly utilised and these are collectively termed “road trains”. Road trains are not currently permitted in Western Europe due to weight limits on the size of vehicles; however, due to the environmental and cost advantages of road trains, it is likely that this will change.
In all these territories there are a large number of small engineering companies building trailers for various tractors employing compressed air operable brakes. Such trailer builders tend to specialize in specific vehicle types, but to meet statutory requirements, it is a common feature that trailers are provided with means which control the braking force signaled from a towing tractor. These trailer braking systems are now invariably electronic braking systems (EBS) having electronic control by an ECU. It is now routine that the electronic braking systems can incorporate features such as stability control. Stability control has proved to be a major safety enhancement.
Tractors are commonly provided with electronic stability control such as ESP®, which can generate an additional brake demand on the trailer but cannot provide full stability control on the trailer, only on the tractor. Trailers are therefore provided with roll stability control (RSP). Trailer Roll stability control monitors the lateral acceleration on the trailer as a build-up of lateral acceleration leads to a rollover of the trailer, as well as providing selective brake application and monitoring wheel speeds to detect any wheel lift which generates abnormal rotational speeds. The commonest rollover situations include where a driver steers rapidly in one direction and then back in the opposite direction, for example to avoid an obstruction on the motorway. In this situation, the ECU is able to make a predictive intervention to stabilize the vehicle by controlling the brake force at either an axle or individual wheel level. The other common rollover situation is where there is a slow build-up of lateral acceleration on the trailer on, for example, a motorway exit, where a small selective brake application to the inside (with respect to the curve) wheels may result in a large change in velocity. In this case, the ECU can apply a large brake effort to stabilize the vehicle.
Known RSP systems suffer from the problem that they cannot simply be extended to road trains as due to the increased size of the vehicle, it may take too long for the lateral acceleration signal to be measured, processed and the brake demand adjusted before the rollover event occurs. This will be particularly the case if the center of gravity of the vehicle is towards the rear of the train.
The present invention therefore seeks to provide a trailer electronic braking system adapted to provide roll stability control for road trains.
According to the invention, there is provided a trailer electronic braking system for motor vehicles having a plurality of trailers, the braking system comprising a braking device capable of generating brake force on an axle on each trailer, the brake force into the brake being controllable by a braking ECU on each trailer, a communication interface being provided so that the braking ECU on a first trailer and the braking ECU on a second trailer are able to communicate with one another. The respective braking ECU on the first and second trailer receive an input from a respective sensor on the first and second trailer adapted to detect lateral acceleration and/or wheel speed, wherein, in the event that one of the sensors detects lateral acceleration and/or a wheel speed indicative of a loss of stability, the sensor generates a signal for actuating stability control, which signal is passed via the communication interface to the braking ECU on the other trailer, so that the other trailer can actuate stability control.
Preferably, the communication interface is a CAN bus or powerline carrier. Preferably, the sensor is a lateral acceleration sensor and/or two or more wheel speed sensors. Preferably, the sensor generates a signal only when the lateral acceleration detected exceeds a predetermined threshold. Preferably, if the sensor on the second trailer detects no lateral acceleration, the brake pressure is not increased. Alternatively, if the sensor of the second trailer detects no lateral acceleration the brake force is increased to a level intermediate to the force on the first trailer. Preferably, the braking ECU monitors the wheel speed on its trailer, wherein stability control is initiated as a function of whether the vehicle is braked or unbraked through a braking intervention by monitoring the rotational wheel speed behaviour. Preferably in a case of a braked vehicle, the brake force is lowered at the brake cylinder of the wheel on the inside of a turn and a stability control event initiated if the rotational speed of the wheel increases by less than a predetermined amount.
The invention advantageously improves vehicle stability control in a road train as the risk of braking the trailer individually can lead to instability in the other trailers on the road train thereby increasing the risk of rollover. The invention also advantageously decreases the time between lateral acceleration on the train being detected and stability control being initiated.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.